#include<stdio.h>
#pragma warning(disable:4996)
int main()
{
	int f = 0;
	int x = 0;
	scanf("%d",&x);
	if (x < 0) { f = -1; }
	else if (x = 0 ) { f = 0; }
	else { f = 2 * x; }
	printf("%d\n", f);
	return 0;

}